Field of the Invention
The present invention relates to a suspension board with circuit and a producing method thereof, to be specific, to a suspension board with circuit used in a hard disk drive and a producing method thereof.
Description of Related Art
A suspension board with circuit including a metal supporting board, a base insulating layer that is formed thereon, and a conductive pattern that is formed thereon such as a wire or the like has been known. The suspension board with circuit is mounted with a magnetic head and is used in a hard disk drive or the like.
The conductive pattern includes a write wire and a read wire. The front end portion of each of the wires is connected to a magnetic head and the rear end portion of each of the wires is connected to an external board. In order to reduce noise in signal transmission, the conductive pattern includes one pair of write wires and one pair of read wires and in each of the write wires and each of the read wires, a differential signal wire has been generally used in which a first wire through which a first electrical signal is transmitted and a second wire through which a second electrical signal that is antiphase with respect to the first electrical signal is transmitted are included.
In the differential signal wire, differential impedance occurs, so that the differential impedance is required to be reduced.
Thus, a structure (interleaved wiring) has been known in which the first wire and the second wire in the one pair of the write wires and the first wire and the second wire in the one pair of the read wires are alternately disposed. In the structure, it is required that the first wire crosses the second wire without contact with each other. That is, it is required that one wire (the first wire) strides over the other wire (the second wire) to be electrically connected thereto.
As such a method, for example, in Japanese Unexamined Patent Publication No. 2012-414217, a suspension board has been disclosed in which electrically conductive metal portions, each of which penetrates through a base insulating layer and connects a first wire to a metal supporting board, are formed at one side of a second wire and at the opposite side thereto with the second wire to be strode over. In the suspension board, the first wire at one side is electrically connected to the first wire at the other side via the electrically conductive metal portion at one side, the metal supporting board, and the electrically conductive metal portion at the other side, so that the first wire is capable of crossing the second wire without contact therewith.
The electrically conductive metal portion is formed into a circular shape in plane view having a diameter that is longer than the length in a widthwise direction of the wire in order to surely connect the first wire to the metal supporting board.
On the other hand, other than in the interleaved wiring, in ground wiring in which the base insulating layer is penetrated through to be grounded to the metal supporting board, the electrically conductive metal portion is also used as an electrically conductive portion that electrically conducts a ground wire to the metal supporting board.